The present invention relates to a fast neutron nuclear reactor cooled by a liquid metal such as sodium, and of the integrated type, in which the primary circuit is contained in the main vessel sealed by a slab.
More specifically, integrated fast neutron nuclear reactors are characterized by the fact that the main vessel contains the reactor core, an inner vessel defining within the main vessel a hot zone filled with relatively hot liquid metal and a cold zone filled with relatively cold liquid metal, at least one pump for circulating the liquid metal between the cold zone and the hot zone across the core and at least one heat exchanger located between the hot and cold zones. Two versions have been proposed for the inner vessel of integrated reactors, such as the Super-Phenix.
The so-called stepped inner vessel described in French Patent Application Nos. 7,308,075 and 7,536,226 by the Applicant Company is the solution used by the Super-Phenix. The step member separates the hot sodium and the cold sodium between the exchanger inlet and outlet and the main vessel is protected by a thermal baffle. This complex structure is very costly, because it requires a large amount of nuclear quality stainless steel.
Another solution consists of confining the hot sodium within a cylindrical vessel having a diameter substantially equal to that of the core and as proposed in French Patent Applications Nos. 7,539,982 and 7,908,793 by the Applicant Company. The hot sodium must then be brought into the exchanger intake by a tight pipe. This pipe and the ferrules ensuring the sealing of this connection are subject to mechanical and thermal stresses, which make their manufacture particularly difficult. To overcome this problem, it is e.g. necessary to duplicate the inner vessel by a baffle leading once again to the disadvantage of the stepped solution.
Another disadvantage common to both internal vessel types is that there are non-negligible heat leaks to the reactor slab as a result of the size of the free hot sodium surface compared with that of the cold sodium.